1. Field of the Invention
The invention concerns the field of lighting devices for automotive vehicles, and more precisely means for driving the supply of power to light sources inside such devices.
2. Description of the Related Art
In the field of lighting devices for automotive vehicles, and particularly light-signaling devices, it is becoming ever more common to use light sources with semiconductor components, such as light emitting diodes, LED, for example. Compared with incandescent or discharge light sources, the use of LEDs makes it possible to create original optical signatures by placing a plurality of LEDs along a predefined contour, for example. Furthermore, the power consumption of LEDs is generally lower than that of traditional light sources. An LED element emits light radiation of a predefined intensity when it carries an electric current of a predefined intensity that is above a threshold value.
In a known manner, a series connection of multiple LEDs is connected as a load for a device for driving the supply of power to the LEDs. Such a device converts an electric current of a first intensity, which is provided in a general manner by an internal current source of the automotive vehicle, such as a battery, into an electric current of a second, different intensity. The voltage applied to the terminals of the series connection needs to be such that all the LEDs in the connection are able to emit light radiation.
For a given lighting function, it is known practice to provide two modes of lighting having different light intensities. One example is front lighting in high beam, HB, and low beam, LB, modes, respectively. It is known practice to implement this type of functionality by connecting two groups of LEDs in series, the LEDs in their entirety being powered by the same means for driving the supply of power. A switch allows one of the two groups of LEDs in the connection to be shorted. When a short circuit is activated, the light intensity emitted by all of the LEDs is reduced since one of the two groups of LEDs does not emit light radiation. This mode corresponds to the low beam mode, for example. The load on the converter is likewise instantaneously reduced when the short circuit is activated. This abrupt change in the load gives rise to large transient current peaks through the LEDs that continue to be powered. It has been observed that these peaks can have intensities of above 4 A and can take place over approximately 20 μs. However, most of the available LED elements can withstand only current peaks up to approximately 2.5 A. In such known implementations, there is therefore a real risk of damage to the light sources.
It has been proposed to absorb the transient peaks in such connections by absorbing the energy in a resistor that is selectively connected in the load circuit by a transistor when a peak is detected. Such systems need to be resized for each connection of the load, however, and represent an overall loss of energy since part of the energy produced is lost in the resistor.